Most of the elements of the periodic table are solids, a few are gases, and there are only two liquid elements at room temperature and pressure. A total of six liquid elements exist between room temperature and body temperature. There are eight liquid elements, if you include predictions for recently-discovered synthetic elements.
Liquid Elements at 25°C
Room temperature is loosely defined as a temperature between 20°C or 25°C. The two liquid elements at room temperature are mercury (symbol Hg and atomic number 80) and bromine (symbol Br and atomic number 35).
Mercury is the only metal that is a liquid at room temperature. It is a shiny, silver metal with a melting point of 234.3210 K (−38.8290 °C, −37.8922 °F) and boiling point of 629.88 K (356.73 °C, 674.11 °F). The reason mercury is a liquid is due to relativistic effects. Basically, the s-shell electrons are moving so quickly around the atomic nucleus that they behave as if they were more massive than slower-moving electrons. As a consequence, mercury atoms bind weakly to each other and are easily driven apart when the temperature rises and kinetic energy increases.
Bromine is the only nonmetallic element on the periodic table that is a liquid near room temperature. Bromine is a halogen that occurs as a reddish-brown liquid as the diatomic molecule Br2. Its melting point is 265.8 K (−7.2 °C, 19 °F), while its boiling point is 332.0 K (58.8 °C, 137.8 °F). Bromine is a liquid because its outer electrons are distant from its nucleus. So, bromine atoms are easily influenced by intermolecular forces, making the element a liquid rather than solid at room temperature.
Elements That Are Liquid 25°C-40°C
At slightly warmer temperatures, four additional elements are liquids, bringing the total of elements that are liquids at ordinary temperatures to six. In order of increasing melting point, these elements are:
- Mercury (234.32 K)
- Bromine (265.8 K)
- Francium (~300 K)
- Cesium (301.59 K)
- Gallium (303.3 K)
- Rubidium (312.46 K)
Mercury, francium, cesium, gallium, and rubidium are metals. Bromine is a nonmetal (halogen).
Francium is the most electropositive of the elements. Its melting point is known, but so little of the element exists it’s unlikely a photograph of the metal in its liquid state will be taken anytime soon.
Cesium is a soft reactive metal. Like francium, it has a high electropositivity or low electronegativity. The reason cesium and francium are soft and have low melting points is due to the size of their atoms, which means the outer electron shell is far from the atomic nucleus. Although cesium does not have the highest atomic number of any element, its atoms are the largest.
Gallium is a gray metal that you can melt in the palm of your hand from body heat. The element is used as a substitute for mercury in the “beating heart” chemistry demonstration. Spoons made from gallium bend when held and melt in hot liquids.
Rubidium is a soft, silver-colored metal. It is reactive and spontaneously ignites in air to form rubidium oxide. Like cesium (and presumably francium), rubidium violently reacts with water.
Predicted Liquid Elements
Copernicium (atomic number 112) and flerovium (atomic number 114) are man-made radioactive elements that researchers predict are liquids at room temperature and pressure. The predicted melting point of copernicium is about 283 K (50 °F), while the predicted melting point of flerovium is 200 K (-100 °F). Both copernicium and flerovium boil and become gases at temperature well beyond room temperature.
More Liquid Elements
Technically, any element can be a liquid. The point at which an element changes from a solid or gas to a liquid depends on its phase diagram. The phase diagram shows that state of matter based on temperature and pressure. Increasing temperature is one way to melt a solid into its liquid, but controlling pressure also works. For example, the halogen chlorine becomes a liquid at room temperature when pressure is increased.
References
- Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). CRC Press. ISBN 978-1439855119.
- Landolt, Hans Heinrich (1890). “Nekrolog: Carl Löwig”. Berichte der deutschen chemischen Gesellschaft. 23 (3): 905–909. doi:10.1002/cber.18900230395
- Mewes, J.-M.; Smits, O. R.; Kresse, G.; Schwerdtfeger, P. (2019). “Copernicium is a Relativistic Noble Liquid”. Angewandte Chemie International Edition. doi:10.1002/anie.201906966
- Mewes, Jan-Michael; Schwerdtfeger, Peter (2021). “Exclusively Relativistic: Periodic Trends in the Melting and Boiling Points of Group 12”. Angewandte Chemie. doi:10.1002/anie.202100486
- Norrby, L.J. (1991). “Why is mercury liquid? Or, why do relativistic effects not get into chemistry textbooks?”. Journal of Chemical Education. 68 (2): 110. doi:10.1021/ed068p110
- Tonkov, E. Yu; Ponyatovsky, E. G. (2005). Phase Transformations of Elements Under High Pressure. CRC Press. Boca Raton. ISBN 0-8493-3367-9.